In the prior art several assembly processes for electronic equipments suitable for large-scale production have been developed. Basically, each assembly process provides for installing one or more electronic devices (e.g., of the Surface-Mounting Technology or SMT type) on an electronic board (e.g., a Printed Circuit Board or PCB).
Generally, each electronic device comprises a chip (or more) of semiconductor material on which a proper electronic component is integrated. The chip is enclosed in a package of insulating material in order to be isolated and protected from the outside environment. The package exposes conducting pins, which are coupled with corresponding conducting terminals of the chip. The pins are soldered to corresponding conducting pads formed on the electronic board. This allows the interaction between the electronic component, comprised in the electronic device, and other electronic devices, mounted on the electronic board in a similar way, through conducting tracks of the electronic board that properly connect the pads one another.
The soldering between the pins of the electronic devices and the pads of the electronic board should be performed homogenously for ensuring proper and/or with optimal performance operation of the electronic complex. At the same time, the soldering should provide a stable mechanical, electrical and thermal connection between the electronic devices and the electronic board.
A very common soldering technique is the reflow soldering. In this case, each electronic device is provisionally fixed to the electronic board using a solder paste (comprising adhesive elements), which is dispensed between the pins of the electronic device and the corresponding pads of the electronic board. Subsequently, the assembly thus obtained is heated for activating a flux comprised in the solder paste, which flux reacts with the metallic material of the tracks and pins thereby removing any oxidized layer thereof. The assembly is then heated up to melt a filler material of the solder paste. Finally, the assembly is cooled down thereby hardening the filler material.
Unfortunately, the chemical reactions of the adhesive elements and of the flux release waste gas that may be trapped in the solder paste during the cooling down thereof. After the hardening of the filler material, such waste gas forms cavities able to reduce a quality of the electrical coupling, of the mechanical coupling and (partially) of the thermal coupling between the pins and the pads. These cavities may reduce the operating efficiency of the electronic complex and generally reduce a useful life thereof.
A probability of entrapment of the waste gas (with the consequent formation of cavities) in the filler material is substantially proportional to an area of the soldering surface of the pins. Indeed, the greater the area of the soldering surface, the greater the chance that the waste gas originated at a central portion of the pin cannot reach an outer region of the filler material (corresponding to the perimeter of the pin) and be dispersed into the surrounding environment before the hardening of the filler material. In the case of SMT electronic devices with pins exposed on a mounting surface of the insulating body on the electronic board (configuration known as “No-Lead” or “Micro-lead”), the negative effect associated with the presence of such cavities is particularly pronounced in pins that are characterized by the passage of a major electric current flow and/or used as heat sinks.